Phase splitting coupling for coaxial transmission lines



R. A. BRADEN Dec. 28, 1948.

PHASE SPLITTING COUPLING FOR COAXIAL TRANSMISSION LINES Filed Sept. 27, 1946 INVENTOR. v Rea(9Afiramlen BY 0% .24,

ATTORNEY Patented Dec. 28, 1948 PHASE .SPLIT'IING COUPLINGJEOR CDAXIA'L TRANSMISSION LIN ES Rene A. Braden, Princeton; N. J-;, cass'ignoruto. Radio Corporation. of America, az'corporatlonof Delaware Application September 27, 1946;"SeriaTNo; 699,68'2' 9 Claims.

This invention relates generally to wave transmission lines and more particularly to coupling networks for connecting coaxial transmission lines to certain types ofloaddevices such, for example, as dipole antennas and the like.

Heretofore, variousmeans have beenemployed for'cmipling'coaxial transmission lines to oppositely phased load devices wherein the required phase reversal currents have been derived by separate half-wave coaxial line arms interposed between the main transmission line and one of the load devices. 7 One' of the principal disadvantages of such auxiliary phasing devices is that high frequency currents are-carried by theex ternal line conductors'in thevicinityof the load, thus providing undesirable radiation fields. Also suchsystems are inherently cumbersome and unsymmetrical in appearance.

The instant-invention contemplates the use of a third coaxial tubular conductor interposed between the inner and outer coaxial conductors of the coaxial transmission line in the vicinity of one of the loads to'be coupled thereto. The outer coaxial line conductor is enlarged inthe vicinity of a complementarily enlarged portionof the intermediate conductor to provide thereb'etween a wave path which is an odd" multiple of onehalf wavelength at the operating frequency longer than the wave pathbetween'the-inner and intermediate coaxial conductors. The dipolesare connected respectively to the inner and intermediate conductors, and thus areenergized by high frequency-currents of opposite phase. In effect, the highfrequency waves propagated alon the transmission line are divided into two portionswhich are efiectively in series in theregion occupied by the intermediate coaxial conductor. Wave reflections onthe linefrom the'intermediate conductor may be minimized-by tapering'the end thereof facing toward the wave generator, such as by terminating the generator end thereof at an angle to the electric field axis. If desired, a quarter wave stub support maybeprovidedat the end of the'three-conductor portion of the line remote from the generator.

Among theobje'cts of the inv'ention are toprovide an improved methodof and means for transforming unbalanced currents'in a coaxial-transmission line to balanced currents for'application to a dipole antenna or similar load devices. Another object is to provide" an improved coaxial lin'e'transformer for coupling a conventional twoconductorcoaxial line to oppositely-phased loads such as a dipole antenna or the like. Anotherobjectis to provide an'improved'coaxial line'network' for coupling a two-conductor coaxial line-"to e. dipole antenna; --and for supporting the-dipole e'le ments with respect to the coaxial-'lineconductors. A furtherobjecti's'to provide an improved-coupling network for coupling a coaxial'transmission line to oppositely-phased load devices suchas dipole'antennas; or the like; wherein substantiaily no extraneous radiation field is providedby the outer coaxial line conductor in thewicinity ofthe balanced load.

The invention will lie-described in greater detail by reference to the accompanying drawing of which .Figure 1=. thereof is; across-sectional, olerationale View of. a; preferred embodiment of the inventionasiapplied tov energization oi a dipole antenna; andiEigure Eris an enlarged fragmentary cross-sectional. View of the righthand portion of theedeyicelof' E'ig. .1.- Similar reference char;- acters -are applied .to-trsimilar elements throughout "the? drawing.

Referring to. Figure 1 of; thedrawing, a coaxial transmission line comprising an inner-conductor I andaeoncentric :outer conductor3 is connected toasonrce, not shown, of high frequency energy. An intermediate tubular conductor 5 having .a tapered end I facingtoward; the source of wave energy is interposed between the coaxial inner and outer transmission'line conductorsl, 3-inzthe immediate vicinity'of a dipoleantenna or other voppositely'phased load devices tobe coupled 'to'the line. The-intermediate conductor Sincludes; an outwardly projecting portion-9; and the outer conductor 3- .also .includesxa complementarily projectingz portion H' yproviding- .desired spacing of the intermediate and outer conductors in the regionot the projectingl -portion 9 of the intermediate vconductor. The'inner surface -3 i of the tubular intermediate conductor 5 is cylindrical and concentric with the :inner line conductor. I. Thus the waverpropagation/path betweentheiouter and intermediate.conductors-3; 5, respectively, is proportioned to belan .odd multipleof one-half inlthe line at the operatingjre uency longerthan the. wave propagation-path .(n \+c) between the intermediate, and inner line conductors 5, I, .respectively, .inthe vicinity of theload; The surge impedance of the concentric line. sectioncomprising;the.. outer and intermediate conductors. .3, 5"may be made uniformthroughoutthelength of the line section by maintaining .constantthe ratio of the inner diameter of the outerconductor. to. the outer diameter of'the intermediate conductor.

A dipole antenna comprising a pair of dipole stubs l5, I1, is connected to the inner and intermediate line conductors I, 5 through suitable apertures IS in the outer coaxial conductor 3. For example, the first dipole I5 is connected to the inner coaxial conductor I and projects outwardly through an aperture 2| in the intermediate conductor 5 and a coincidental one of the apertures [9 in the outer conductor 3. In order properly to guide the waves A propagated between the inner and intermediate conductors through the field B between the intermediate and outer conductors, the intermediate conductor includes an outwardly projecting sleeve 23 having an annular end ring 25. The sleeve 23 and ring 25 effectively isolate the dipole stub l5 from the wave energy B propagated between the intermediate and outer conductors. Similarly, the other dipole stub 17 passes through the other aperture l9 in the outer coaxial conductor 3 and is connected to the intermediate conductor 'l, at a point diametrically opposite to the point of connection of the dipole stub l5.

In order to support the dipoles and the three coaxial conductors I, 3, 5 in proper relative position, the ends of the three coaxial conductors may be connected together by an annular conductive plug 21 at a point any odd number of quarter wavelengths in the line at the operating frequency from the dipole antenna stubs l5, l1. It should be understood that any other type of oppositely-phased loads, other than the dipole antenna described heretofore, may be connected in a similar manner to the inner andintermediate conductors.

The operation of the system may be more clearly understood by reference toFigure 2 of the drawing wherein the wave energy A propagated between the inner and intermediate conductors I, 5 is indicated by the dash line arrows 29, and the oppositely phased wave energypropagated betweenthe intermediate and outer conductors 5, 3 is indicated by the solid line arrows 3 I. The waves A are guided out by the inner end of the dipole stub I5 through the space between the dipole stub and the coaxial sleeve 23 andare launched into space as an electromagnetic wave r radiation. The-Wave A therefore may be considered .as existing in the space between the inner conductorl and the inside surface of the intermediate conductor 5 and the inside surface of the sleeve 23.

Likewise, the waveB, which is delayed onehalfperiod from the wave A, may be considered as traveling in the space between the outside surface of the intermediate conductori and the inside surface of the outer conductor 3. The wave'B, therefore, travels out to the end of the second dipole stub l1 and is radiated intospac as a second electromagnetic wave which is oppositely-phase with respect'to the waves radiated by the first dipole stub l5.

It will be apparent that currents flow on the outer surface of the outer conductor 3 only in the vicinity of the second dipole stub I! and. possibly within a very limited region between the outer conductor 3 and the under surface of the annular ring 25. Otherwise all of the currents in the line flowing as a result of propagation of the waves B travel on the inner surface of theouter conductor 3 and the outer surface of the intermediate conductor 5- L kewise the currents in the line re- 4. sulting from propagation of the wave energy A travel only on the inner surface of the intermediate conductor 5 and the outer surface of the center conductor l. The sleeve 23 and annular ring 25 effectively shield the first dipole stub [5 from currents traveling on the outer conductor 3.

Thus the invention disclosed comprises an improved coaxial line coupling network for coupling a two conduct-or concentric line to oppositelyphased load devices, such as antenna dipoles, wherein the coupling structure is completely enclosed Within a shielding portion of the outer transmission line conductor, and support for the load and the ends of the line conductors is provided by a quarter wave coaxial line stub. Oppositely phased currents for the antenna or loads are provided by the insertion of an intermediate coaxial conductor between the inner and outer coaxial line conductors wherein projecting portions of the intermediate and outer conductors provide the required phase delay with respect to the directly propagated wave energy. The oppositely phased waves in the vicinity of the antenna are segregated by a radially extending sleeve surrounding and coaxial with one of the dipole stubs in the region where it projects through the space between the intermediate and outer line conductors.

I claim as my invention:

1. A network for coupling a transmission line having coaxial inner andouter conductors to oppositely phased load devices including a portion of said outer line conductor having a larger diameter than the remainder thereof, a third coaxial tubular conductor interposed between said inner and outer conductors, said third conductor also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and third conductorsbeing aligned to provide with said inner and outer conductorstwo concentric lines differing in length by substantially an odd number of one-half wavelengths in the line at the operating frequency, and means for connecting said load devices respectively to said inner and third conductors. 1

2. Apparatus according to claim 1 wherein the end of saidthird conduct-or remote from said loads is tapered to reduce wave reflections in said transmission line. l

3. A network for coupling a transmission line having coaxial inner and outer. conductors to a pair of dipole antenna stubs including a portion of said outer line conductor having a larger diameter than the remainder thereof, a third 00- axial tubular conductor interposed between said inner and outer conductors, said third conductor also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and third conductors being aligned to provide with said inner and outer conductors two concentric lines having substantially uniform surge impedances along the lengths thereof, said line lengths differing by substantially an odd'number of one-half wavelengths in the line at the operating frequency, and means for connecting said dipole antenna between said innerandthird conductors.

4. A network for coupling a transmission line having coaxial inner and outer conductors to oppositely phased load devices including a portion of said outer line conductor having a larger diameter than the remainder thereof, a third coaxial tubular conductors interposed between said i n r amu et q r i iors said. th rd p uqtor.

also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and third conductors being aligned to provide with said inner and outer conductors two concentric lines having substantially uniform spacing along the lengths thereof, said line lengths difiering by substantially an odd number of one-half wavelengths in the line at the operating frequency, and means for connecting said load devices to said inner and third conductors.

5. A network for coupling a transmission line having coaxial inner and outer conductors to a dipole antenna including a portion of said outer line conduct-or having a gradually increasing larger diameter than the remainder thereof, a third coaxial tubular conductor interposed between said inner and outer conductors, said third conductor also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and third conductors being aligned to provide with said inner and outer conductors two concentric lines differing in length by substantially an odd number of one-half wavelengths in the line at the operating frequency, means for connecting said antenna di poles to said inner and third conductors at points substantially an odd number of quarter wavelengths from the ends of said conductors, and means connecting together and supporting said ends of all of said conductors.

6. A network for coupling a transmission line having coaxial inner and outer conductors to a pair of dipoles including a portion of said outer line conductor having a larger diameter than the remainder thereof, a third coaxial tubular conductor interposed between said inner and outer conductors, said third conductor also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and third conductors being aligned to provide with said inner and outer conductors two concentric lines differing in length by substantially an odd number of one-half Wavelengths in the line at the operating frequency, means for separately connecting said dipoles to said inner and third conductors, and means shielding one of said dipoles from the field in said line energizing the other of said dipoles, said dipoles being energized in opposite phase.

7. A network according to claim 6 wherein the end of said third conductor remote from said load is tapered to reduce wave reflections in said transmission line, said dipoles are connected to said conductors at points an odd number of quarter wavelengths from the ends thereof remote from said tapered portion, and means for connecting together and supporting said ends of all of said conductors remote from said tapered portion and said dipoles.

8. A network for coupling a source of high frequency energy through a transmission line having coaxial inner and outer conductors to a pair of dipoles including a portion of said outer line conductor having a larger diameter than the remainder thereof, an intermediate tubular conductor interposed between said inner and outer conductors, said intermediate conduct-or also having a portion having a larger diameter than the remainder thereof, said larger diameter portions of said outer and intermediate conductors being aligned to provide with said inner and outer conductors two concentric lines differing in length by substantially an odd number of onehalf wavelengths in the line at the operating frequency, means for connecting said dipoles respectively to said inner and intermediate conductors at points an odd number of quarter Wavelengths from the ends thereof remote from said source, means conductively terminating and supporting the ends of all of said conductors remote from said source whereby said load is effectively balanced with respect to said outer line conductor, and means comprising a cylindrical sleeve and an annular ring coaxial with one of said dipoles and connected to said intermediate conductor for shielding said last-mentioned dipole from wave energy propagated between said intermediate and outer line conductors.

9. A network for coupling a transmission line having coaxial inner and outer conductors to oppositely phased load devices, including a portion of one of said coaxial line conductors having a different diameter than the remainder thereof, a third coaxial tubular conductor interposed between said inner and outer conductors, said third conductor also having a portion having a dinerent diameter than the remainder thereof, said different diameter portions of said coaxial and REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,266,502 Lindenblad Dec.16, 1941 2,275,646

Peterson Mar. 10, 1942 

